Battery cooling structure

ABSTRACT

A battery cooling structure includes a cooling plate and an electrically insulative sheet. The cooling plate is to support a cooling surface of a battery module to cool the battery module including a plurality of battery cells arranged side by side. The electrically insulative sheet has an electrical non-conductivity and is disposed between the cooling surface of the battery module and the cooling plate to transfer heat from the cooling surface to the cooling plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2011-269836, filed Dec. 9, 2011, entitled“Battery Cooling Structure.” The contents of this application areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present application relates to a battery cooling structure.

Discussion of the Background

In the case where a cooling surface of a battery module is supported bya hollow cooling plate in which a refrigerant flows, and the batterymodule is cooled by transferring heat generated in the battery modulefrom the cooling surface to the cooling plate, a small gap isunavoidably formed between the cooling surface of the battery module,which is a rigid body, and the cooling plate, which also is a rigidbody. The gap suppresses heat transference between the cooling surfaceand the cooling plate, thereby degrading the performance with which thebattery module is cooled.

In order to solve the above-described problem, the following technology,which is disclosed in Japanese Unexamined Patent Application PublicationNo. 2011-34775, is known. That is, a heat transfer sheet, which isdeformable and has a good heat transfer property, is sandwiched betweena cooling surface of a battery module and a cooling plate, so that thegap between the cooling surface of the battery module and the coolingplate is eliminated by deformation of the heat transfer sheet. Thisfacilitates heat transfer from the cooling surface to the cooling plate,thereby improving performance with which the battery module is cooled.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a battery coolingstructure includes a cooling plate and an electrically insulative sheet.The cooling plate is to support a cooling surface of a battery module tocool the battery module including a plurality of battery cells arrangedside by side. The electrically insulative sheet has an electricalnon-conductivity and is disposed between the cooling surface of thebattery module and the cooling plate to transfer heat from the coolingsurface to the cooling plate.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 is a perspective view of a battery module (first embodiment).

FIG. 2 is an exploded perspective view of the battery module (firstembodiment).

FIG. 3 is a perspective view of the vertically inverted battery module(first embodiment).

FIG. 4 is an enlarged view of part IV in FIG. 3 (first embodiment).

FIG. 5 is a sectional view of the structure illustrated in FIG. 4 takenalong line V-V in FIG. 4 (first embodiment).

FIG. 6 is a sectional view of the structure illustrated in FIG. 4 takenalong line VI-VI in FIG. 4 (first embodiment).

FIGS. 7A to 7C illustrate the shape of a heat transfer sheet (firstembodiment).

FIG. 8 is a diagram of the structure illustrated in FIG. 2 seen from adirection indicated by an arrow VIII in FIG. 2 (first embodiment).

FIG. 9 illustrates how the structure illustrated in FIG. 5 works (firstembodiment).

FIG. 10 illustrates how the structure illustrated in FIG. 6 works (firstembodiment).

FIGS. 11A to 11C illustrate alternative embodiments of a positioninghole (second to fourth embodiments).

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

Embodiments of the present application will be described below withreference to FIGS. 1 to 11C.

As illustrated in FIGS. 1 and 2, a battery pack 11, which is to beinstalled on an electric vehicle, includes a cooling plate 12 and aplurality of battery modules 13, which are supported on the coolingplate 12. Two battery modules 13 and part of the cooling plate 12 areillustrated in FIGS. 1 and 2. Although two battery modules 13, each ofwhich has substantially the same structure, are integrated into a singleunit in the present embodiment.

The battery modules 13 each structured such that a plurality of (12 inthe embodiment) box-shaped battery cells 14 are arranged side by sidewith intermediate holders 15 sandwiched between the battery cells 14 andend holders 16 disposed on the outer sides of two battery cells 14located at both ends in a direction in which the battery cells 14 arearranged. The intermediate holders 15 and the end holders 16 are formedof synthetic resin.

As illustrated in FIGS. 3 to 6, each intermediate holder 15 having anH-shaped horizontal section, has a plate-shaped holder body portion 15a, a pair of side flanges 15 b, and a lower flange 15 c. In eachintermediate holder 15, the holder body portion 15 a is sandwichedbetween two adjacent battery cells 14, the side flanges 15 b protrudefrom left and right side edges of the holder body portion 15 a towardboth sides in the battery cell 14 arranging direction, and the lowerflange 15 c protrudes from a lower edge of the holder body portion 15 atoward both sides in the battery cell 14 arranging direction. The sideflanges 15 b of the adjacent intermediate holders 15 are engaged withone another, thereby regulating the mutual positional relationshipsbetween the intermediate holders 15, and as a result, the mutualrelationships among the plurality of battery cells 14 are regulated. Thewidth of the lower flange 15 c is smaller than that of the side flanges15 b. Thus, in a state in which the adjacent side flanges 15 b of theintermediate holders 15 are engaged with one another, the lower flanges15 c are not engaged with one another, and lower surfaces (coolingsurfaces 14 a, which will be described later) of the battery cells 14are exposed in areas between the lower flanges 15 c.

Each end holder 16, which has a staple-shaped horizontal section, has aplate-shaped holder body portion 16 a and a pair of side flanges 16 b.The holder body portions 16 a are each in contact with an outer surfaceof a corresponding one of the battery cells 14 located at the outersides in the battery cell 14 arranging direction. The side flanges 16 bprotrude from left and right side edges of the holder body portion 16 afurther toward the inside than the respective side edges in the batterycell 14 arranging direction. The side flange 16 b are each engaged withthe corresponding side flange 15 b of the adjacent intermediate holders15, thereby regulating the positional relationships among all theintermediate holders 15 and the end holders 16.

Referring back to FIGS. 1 and 2, a pair of end plates 17 are superposedon outer surfaces of the pair of end holders 16 of each battery module13 in the battery cell 14 arranging direction. The pair of end plates 17are fastened by a fastening belt 18, thereby firmly integrating 12battery cells 14, 11 intermediate holders 15, and two end holders 16with one another. Two fastening belts 18 are shared by two batterymodules 13. Surfaces of the battery cells 14, the intermediate holders15, and the end holders 16 in contact with one another are secured toone another with adhesive.

A busbar plate 19, which holds a plurality of busbars (not shown), issecured to an upper surface of each battery module 13. Terminals of thebattery cells 14 are electrically connected to one another through thebusbar plate 19. Upper surfaces of two battery modules 13 arranged sideby side are covered with a common cover 20 formed of synthetic resin.

The lower surfaces of 12 battery cells 14 included in each batterymodule 13, the lower surfaces defining a lower surface of the batterymodule 13, form the cooling surfaces 14 a that oppose an upper surfaceof the cooling plate 12 (see FIGS. 3 to 6). A rectangular heat transfersheet 21 is sandwiched between these cooling surfaces 14 a and the uppersurface of the cooling plate 12. The heat transfer sheet 21 is formed ofa synthetic resin having a good heat transfer property (for example,silicone rubber) and deformable into an arbitrary shape when a pressureis applied to the heat transfer sheet 21 so as to compress the heattransfer sheet 21. The heat transfer sheet 21 has a property, with whichsurfaces thereof are sticky (adhering property).

An electrically insulative sheet 22 is disposed between a lower surfaceof the heat transfer sheet 21 and the upper surface of the cooling plate12. The electrically insulative sheet 22 is formed of a synthetic resinhaving an electrical non-conductivity and water repellency such aspolypropylene (PP) or polyphenylene sulfide (PPS). The electricallyinsulative sheet 22 has a shallow tray shape and has a bottom wallportion 22 a and side wall portions 22 b that extend upward from thebottom wall portion 22 a. A lower portion of the battery module 13 isfitted into the electrically insulative sheet 22. Accordingly, an uppersurface of the heat transfer sheet 21 is in contact with the coolingsurfaces 14 a of the battery cells 14, and the lower surface of the heattransfer sheet 21 is in contact with an upper surface of theelectrically insulative sheet 22. The electrically insulative sheet 22,the thickness of which is very small, substantially does not preventheat from being transferred.

The cooling plate 12 is a hollow metal member having a good heattransfer property. The cooling plate 12 has a refrigerant path 12 cdefined by an upper wall portion 12 a and a lower wall portion 12 b, therefrigerant path 12 c allowing a refrigerant (for example, cooling air)to flow therethrough. Cooling air is sucked by a cooling fan (not shown)so as to flow through the refrigerant path 12 c of the cooling plate 12.Heat is transferred from the cooling surfaces 14 a of the battery cells14 through the heat transfer sheet 21 and the electrically insulativesheet 22 to the upper wall portion 12 a and is subjected to heatexchange with the cooling air, thereby cooling the battery cells 14.

As illustrated in FIGS. 7A and 7C, the heat transfer sheet 21 has arectangular shape having its long sides in the battery cell 14 arrangingdirection and its short sides in a direction perpendicular to thebattery cell 14 arranging direction. The thickness of the heat transfersheet 21 is uniform along the short sides and varied along the longsides. That is, in the heat transfer sheet 21, a thickness T1 in acentral portion in a long side direction is large (for example, 4.1 mm)and a thickness T2 in both end portions in a long side direction issmall (for example, 3.1 mm), and the thickness is continuously changedbetween T1 and T2.

The heat transfer sheet 21 has a total of 33 positioning holes 21 aformed in three rows in the long side direction. A lower surface of thelower flange 15 c of each intermediate holder 15, the intermediateholder 15 being sandwiched between the pair of adjacent battery cells14, opposes three positioning holes 21 a. The positioning holes 21 aeach have a square shape with its corners rounded. The width of thelower flanges 15 c is smaller than the width of the positioning holes 21a. Thus, both side edges of each lower flange 15 c are visible throughthe corresponding positioning holes 21 a.

A total of 11 positioning grooves 21 b, which extend parallel to theshort sides of the heat transfer sheet 21, are formed in the uppersurface of the heat transfer sheet 21, that is, in the surface oppositethe cooling surfaces 14 a of the battery cells 14. In the presentembodiment, three positioning holes 21 a are superposed on eachpositioning groove 21 b. The lower flanges 15 c of the intermediateholders 15 protrude downward beyond the cooling surfaces 14 a of thebattery cells 14. These lower flanges 15 c are each fitted into acorresponding one of the positioning grooves 21 b. In the heat transfersheet 21, the widths of 11 positioning grooves 21 b are varied in astep-by-step manner such that a width W1 in a portion where thethickness of the heat transfer sheet 21 is large (central portion in thelong side direction) is small and a width W2 in portions where thethickness of the heat transfer sheet 21 is small (both end portions inthe long side direction) is large.

A total of 12 first air bleeding grooves 21 c are formed on the uppersurfaces of the heat transfer sheet 21 along central portions of thecooling surfaces 14 a of the battery cells 14. Thus, 11 positioninggrooves 21 b and the 12 first air bleeding grooves 21 c are alternatelyformed so as to be parallel to one another. A total of 24 second airbleeding grooves 21 d are formed on the lower surface of the heattransfer sheet 21 so as to extend along intermediate positions betweenthe positioning grooves 21 b and the first air bleeding grooves 21 csuch that two second air bleeding grooves 21 d are formed betweenadjacent first air bleeding grooves 21 c. Two second air bleedinggrooves 21 d oppose the cooling surface 14 a of each battery cell 14,and the positions of the second air bleeding grooves 21 d are shifted inthe long side direction so as not to superposed on the positions of thepositioning grooves 21 b and the positions of the first air bleedinggrooves 21 c. The sectional area of the second air bleeding grooves 21 dis set to be greater than that of the first air bleeding grooves 21 c.

Ends of the positioning grooves 21 b, the first air bleeding grooves 21c, and the second air bleeding grooves 21 d reach the pair of long sidesof the heat transfer sheet 21 so as to form openings.

The intermediate holders 15 and the end holders 16 respectively haveprotruding wall portions 15 d and 16 c formed throughout lower endsthereof. The protruding wall portions 15 d and 16 c downwardly extendbeyond the cooling surfaces 14 a of the battery cells 14 and protrude soas to extend toward areas under the cooling surfaces 14 a. Theprotruding wall portions 15 d and 16 c are formed so as to surround anouter periphery of the heat transfer sheet 21 with small gaps α (seeFIGS. 4 to 6) formed between the protruding wall portions 15 d and 16 cand the heat transfer sheet 21. A protruding height of the protrudingwall portions 15 d and 16 c below the cooling surfaces 14 a is set to besmaller than the thickness of the heat transfer sheet 21.

As illustrated in FIGS. 3 and 8, three retainers 22 c protrude from anupper edge of the side wall portion 22 b corresponding to each of a pairof long sides of the electrically insulative sheet 22. Among the threeretainers 22 c, the long side of a retaining hole 22 d of the retainer22 c at the center is short and the long side of two retaining holes 22e of the retainers 22 c at both ends is long. Retaining protrusions 15 ethat can be retained in the retaining holes 22 d and 22 e of theelectrically insulative sheet 22 protrude on both side surfaces of threeintermediate holders 15 disposed at positions corresponding to theretainers 22 c.

Next, operation of the embodiment having the above-described structurewill be described.

As illustrated in FIG. 3, when assembly of each of the two batterymodules 13 is completed, the heat transfer sheet 21 is positioned withrespect to the cooling surfaces 14 a of the battery cells 14 of eachbattery module 13 and attached to the cooling surfaces 14 a using theadhesive property of the heat transfer sheet 21. At this time, when theheat transfer sheet 21 is attached to a wrong position and removed fromthe cooling surfaces 14 a, the flexible heat transfer sheet 21 may bedamaged. In order to avoid damage to the heat transfer sheet 21, theheat transfer sheet 21 needs to be attached to a right position througha single attaching operation.

In order to attach the heat transfer sheet 21 to the right positionthrough a single attaching operation, while visually checking thecooling surfaces 14 a of the battery cells 14 through the positioningholes 21 a of the heat transfer sheet 21, that is, visually checking thelower flanges 15 c of the intermediate holders 15 visible together withthe cooling surfaces 14 a of the battery modules 13, an operatorpositions the heat transfer sheet 21 with respect to the coolingsurfaces 14 a and attaches the heat transfer sheet 21 to the coolingsurfaces 14 a so that the lower flanges 15 c are positioned at centralportions of the positioning holes 21 a (see FIG. 4). Since there areplurality of the positioning holes 21 a formed in a distributed mannerover the entire cooling surfaces 14 a, the heat transfer sheet 21 ishighly precisely positioned. At this time, since the width of the lowerflanges 15 c is smaller than the width of the positioning holes 21 a,both the side edges of each lower flange 15 c are visible through thecorresponding positioning holes 21 a. Thus, precision with which theheat transfer sheet 21 is positioned is further improved.

As can be clearly seen from FIGS. 4 to 6, attachment of the heattransfer sheet 21 to the cooling surfaces 14 a, which would beobstructed by the lower flanges 15 c of the intermediate holders 15protruding beyond the cooling surfaces 14 a of the battery modules 13,can be performed without trouble by fitting the lower flanges 15 c intothe positioning grooves 21 b formed in the upper surface of the heattransfer sheet 21. At this time, by fitting the lower flanges 15 c intothe positioning grooves 21 b, the heat transfer sheet 21 is physicallypositioned, thereby further improving precision with which the heattransfer sheet 21 is positioned. Furthermore, when the heat transfersheet 21 is attached, the gaps α are formed between the outer peripheryof the heat transfer sheet 21 and the protruding wall portions 15 d and16 c of the intermediate holders 15 of the battery modules 13 and theend holders 16 of the battery modules 13. Thus, even when the heattransfer sheet 21 is attached at a slightly misaligned position, theheat transfer sheet 21 does not interfere with the protruding wallportions 15 d and 16 c.

Since the corners of the positioning holes 21 a are rounded, even if theheat transfer sheet 21 is attached to a wrong position and removed so asto be attached again, a situation in which the heat transfer sheet 21breaks due to stress concentrated in the corners of the positioningholes 21 a can be avoided.

When attaching the heat transfer sheet 21 to the cooling surfaces 14 aof the battery modules 13, air may be trapped between the upper surfaceof the heat transfer sheet 21 and the cooling surfaces 14 a of thebattery modules 13. This may prevent tight contact of the heat transfersheet 21 with the cooling surfaces 14 a at positions where the air istrapped, thereby forming a heat insulation layer formed by the air anddegrading the heat transfer property. However, because of the pluralityof first air bleeding grooves 21 c formed in the upper surface of theheat transfer sheet 21, the trapped air is discharged through the firstair bleeding grooves 21 c to the outside, thereby making the heattransfer sheet 21 in tight contact with the cooling surfaces 14 a. Thus,the heat transfer property can be improved. Here, it is clear that thepositioning grooves 21 b also function as air bleeding holes.

When the heat transfer sheet 21 has been attached to the coolingsurfaces 14 a of the battery modules 13 as described above, asillustrated in FIGS. 1, 3, and 4, the lower portions of the batterymodules 13 is fitted into the tray-shaped electrically insulative sheet22, and six retaining protrusions 15 e of the side flanges 15 b of threeintermediate holders 15 are retained in the retaining holes 22 d and 22e of six retainers 22 c of the electrically insulative sheet 22, therebyintegrating the electrically insulative sheet 22 with the batterymodules 13 so as not to drop from the battery modules 13. Work forretaining the retaining protrusions 15 e in the retaining holes 22 d and22 e is easily performed since the electrically insulative sheet 22 isthin and arbitrarily deformable.

Since the battery module 13 is formed of 12 battery cells 14 arrangedside by side, the distance D between six retaining protrusions 15 e onthe side surfaces of the intermediate holders 15 (see FIGS. 3 and 8)unavoidably varies due to a cumulative tolerance. However, the width offour retaining holes 22 e located at both ends in the long sidedirection of the electrically insulative sheet 22 is set to be largerthan the width of corresponding four retaining protrusions 15 e. Thus,when four retaining protrusions 15 e at both the ends in the long sidedirection of the battery module 13 are retained in four retaining holes22 e at both the ends in the long side direction of the electricallyinsulative sheet 22 after two retaining protrusions 15 e at the centerin the long side direction of the battery module 13 have been retainedin two retaining holes 22 d at the center in the long side direction ofthe electrically insulative sheet 22, the retaining protrusions 15 e canbe smoothly retained in the retaining holes 22 d and 22 e despite theabove-described variation in the distance D between the retainingprotrusions 15 e.

In the present embodiment, by positioning the electrically insulativesheet 22 with reference to two retaining holes 22 d at the center in thelong side direction, the cumulative tolerance in the thicknesses of thebattery cells 14 are distributed in two directions. Thus, misalignmentbetween the four retaining holes 22 e at both the ends in the long sidedirection and the corresponding four retaining protrusions 15 e can bereduced as much as possible. If the electrically insulative sheet 22 ispositioned with reference to two retaining holes 22 e at one end in thelong side direction, the amount by which two retaining holes 22 e at theother end in the long side direction and the corresponding two retainingprotrusions 15 e are misaligned is doubled.

When the electrically insulative sheet 22 has been attached to eachbattery module 13 as described above, as illustrated in FIG. 1, thebattery modules 13 are placed on the upper wall portion 12 a of thecooling plate 12, and attaching flanges 17 a of the end plates 17 aresecured to attaching bosses 12 d of the cooling plate 12 with bolts 23inserted therethrough. As a result, as illustrated in FIGS. 9 and 10,the weight of the battery modules 13 is applied to the heat transfersheet 21, thereby compressing the heat transfer sheets 21 in the up-downdirection. This eliminate gaps between the upper surfaces of the heattransfer sheets 21 and the cooling surfaces 14 a of the battery modules13 and gaps between the lower surfaces of the heat transfer sheets 21and the upper wall portion 12 a of the cooling plate 12. Thus, heat isefficiently transferred from the battery modules 13 to the cooling plate12, thereby improving the performance with which the battery modules 13are cooled.

The bottom wall portions 22 a of the electrically insulative sheets 22are present between the lower surfaces of the heat transfer sheets 21and the upper wall portion 12 a of the cooling plate 12. However, sincethe electrically insulative sheets 22 are formed of very thin syntheticresin, and accordingly, easily deformable, the presence of theelectrically insulative sheets 22 does not lead to formation of gapsthat prevent heat from being transferred.

When air is trapped between the lower surfaces of the heat transfersheets 21 and the upper wall portion 12 a of the cooling plate 12, moreexactly, between the lower surfaces of the heat transfer sheet 21 andthe upper surfaces of the electrically insulative sheets 22, the air mayprevent the heat transfer sheets 21 from tightly contacting the upperwall portion 12 a of the cooling plate 12, and the air may serve as aheat insulation layer that degrades the heat transfer property. However,because of the plurality of second air bleeding grooves 21 d formed inthe lower surfaces of the heat transfer sheets 21, the trapped air isdischarged through the second air bleeding grooves 21 d to the outside,thereby making the heat transfer sheets 21 in tight contact with theupper wall portion 12 a of the cooling plate 12. Thus, the heat transferproperty can be improved.

When the heat transfer sheets 21 are compressed in the up-downdirection, the outer periphery of each heat transfer sheet 21 tends toexpand outward. However, since the protruding wall portions 15 d of theintermediate holders 15 and the protruding wall portions 16 c of the endholders 16 oppose the outer periphery of the heat transfer sheet 21 withthe gaps α therebetween, the outer periphery of the heat transfer sheet21 is blocked by the protruding wall portions 15 d and 16 c andprevented from expanding outward beyond the outer periphery of thebattery module 13. The heat transfer sheets 21, which are prevented fromexpanding outward by the protruding wall portions 15 d and 16 c, expandinward so as to press the positioning holes 21 a and reduce the size ofthe positioning holes 21 a, thereby decreasing the opening areas of thepositioning holes 21 a.

It is intended that the positioning holes 21 a are formed at positionscorresponding to the lower flanges 15 c of the intermediate holders 15so that the positioning holes 21 a do not prevent heat from beingtransferred from the cooling surfaces 14 a. In addition, when theopening areas of the positioning holes 21 a are reduced in a way asdescribed above, and portions of the cooling surfaces 14 a exposed onboth sides of the lower flanges 15 c of the intermediate holders 15 arecovered by the heat transfer sheets 21, degradation of the heat transferproperty caused by formation of the positioning holes 21 a can bereduced as much as possible.

As is the case with the positioning holes 21 a, the positioning grooves21 b, the first air bleeding grooves 21 c, and the second air bleedinggrooves 21 d are also compressed and eliminated, or the sectional areasthereof are reduced. This allows degradation of the heat transferproperty caused by formation of the positioning grooves 21 b, the firstair bleeding grooves 21 c, and the second air bleeding grooves 21 d tobe reduced as much as possible.

Although the lower surface of each heat transfer sheet 21 is entirely incontact with the upper wall portion 12 a of the cooling plate 12, theparts of the upper surface of the heat transfer sheet 21 correspondingto the lower flanges 15 c of the intermediate holders 15 are not incontact with the cooling surfaces 14 a. Thus, a heat transfer area ofthe upper surface is smaller than that of the lower surface, therebydegrading the heat transfer property. However, according to the presentembodiment, when the heat transfer sheet 21 is compressed, the first airbleeding grooves 21 c, which are formed in the upper surface of the heattransfer sheets 21 and have small sectional areas, are completelyeliminated while the second air bleeding grooves 21 d, which are formedin the lower surface of the heat transfer sheet 21 and have largesectional areas, are not completely eliminated. Thus, the heat transferarea of the lower surface is decreased by the area corresponding to theremaining second air bleeding grooves 21 d. As a result, in each heattransfer sheet 21, the heat transfer area of the upper surface and theheat transfer area of the lower surface become substantially equal toeach other, and accordingly, the heat transfer property can be preventedfrom being degraded.

In each heat transfer sheet 21, the positioning grooves 21 b and thefirst air bleeding grooves 21 c in the upper surface are arrangedparallel to the second air bleeding grooves 21 d in the lower surface sothat the positioning grooves 21 b and the first air bleeding grooves 21c do not intersect the second air bleeding grooves 21 d in plan view. Inaddition, the positioning grooves 21 b and the first air bleedinggrooves 21 c in the upper surface are offset from the second airbleeding grooves 21 d in the lower surface in plan view so that thepositioning grooves 21 b and the first air bleeding grooves 21 c do notsuperpose on the second air bleeding grooves 21 d in the up-downdirection. This arrangement can prevent these grooves from superposingon one another in the up-down direction or intersecting one another.Thus, a situation in which the thickness of part of the heat transfersheet 21 is decreased can be prevented from occurring.

When the heat transfer sheet 21 is compressed, spaces formed between thepositioning grooves 21 b of the heat transfer sheet 21 and the lowerflanges 15 c of the intermediate holders 15 are eliminated. However,these spaces may remain. The reason is that these spaces, which opposethe lower flanges 15 c, do not affect the heat transfer property of theheat transfer sheet 21. Furthermore, because of the presence of thesespaces, contact pressure between the upper surface of the heat transfersheet 21 and the cooling surfaces 14 a is increased, and accordingly,gaps can be prevented from being formed between the upper surface of theheat transfer sheet 21 and the cooling surfaces 14 a.

Since the cooling plate 12 is a hollow member with the refrigerant path12 c defined therein, the upper wall portion 12 a is bent into adownward arc shape by an application of the weight of the batterymodules 13 to the upper wall portion 12 a. This causes the distancebetween the cooling surfaces 14 a of each battery module 13 and theupper wall portion 12 a to be increased in the central portion in thelong side direction relative to that in both the end portions in thelong side direction. As a result, when it is assumed that the heattransfer sheets 21 each have a uniform thickness, contact pressure ofthe heat transfer sheet 21 in the central portion in the long sidedirection is decreased, and accordingly, the heat transfer sheet 21cannot be sufficiently compressed. This may allow a gap to be formed inlow-contact-pressure parts, thereby degrading the heat transferproperty.

However, according to the present embodiment, as illustrated in FIG. 7B,the thickness of the heat transfer sheet 21 is large in the centralportion in the long side direction and small in both the end portions ina long side direction. Thus, even when the upper wall portion 12 a ofthe cooling plate 12 is bent into a downward arc shape, a uniformcontact pressure can be applied to the entire area of the heat transfersheet 21 so as to compress the central portion in the long sidedirection similarly to the both the end portions in the long sidedirection. Thus, the gap is prevented from being formed between the heattransfer sheet 21 and the upper wall portion 12 a, and the heat transferproperty can be prevented from being degraded.

When the upper wall portion 12 a of the cooling plate 12 is bent into adownward arc shape, the central portions of the battery modules 13 inthe long side direction, the battery modules 13 being supported by theupper wall portion 12 a, tend to be bent into a downward arc shape.However, since the thickness of each heat transfer sheet 21 is increasedat its central portion in the long side direction, a reaction load thatpushes up the central portion in the long side direction of each batterymodule 13 is increased, and accordingly, bending of the battery module13 can be suppressed. Furthermore, as illustrated in FIGS. 7B and 7C,the widths of the positioning grooves 21 b formed in the upper surfaceof each heat transfer sheet 21 become smaller as the positions of thepositioning grooves 21 b become closer to the central portion in thelong side direction. Thus, the central portion in the long sidedirection of the heat transfer sheet 21 is not easily compressed, andaccordingly, the upward reaction load at the central portion increases.As a result, bending of the battery modules 13 can be more reliablysuppressed.

The temperatures of the battery cells 14 increase when charging ordischarging the battery cells 14 and decrease when charging ordischarging of the battery cells 14 is stopped. When the temperatures ofthe battery cells 14 decrease, moisture in the air condenses and adheresonto the surfaces of the battery modules 13. When the water havingcondensed flows downward due to gravity and reaches the cooling plate12, a ground fault in which an electrode of the battery cell 14 iselectrically connected to the cooling plate 12 may occur.

However, according to the present embodiment, the electricallyinsulative sheet 22 disposed on the lower side of each heat transfersheet 21 is formed to have a tray shape provided with the side wallportions 22 b that extend upward from the bottom wall portion 22 a. Thisallows the electrically insulative sheet 22 to hold the water havingcondensed therein and prevents the water having condensed from flowingtoward the cooling plate 12. Thus, occurrence of the ground fault can bereliably prevented. Furthermore, since each electrically insulativesheet 22 is formed of a water-repellent material, the water havingcondensed on the surface of the electrically insulative sheet 22 isformed into separate drops. Thus, a situation in which the batterymodules 13 are electrically connected to the cooling plate 12 can bemore effectively prevented.

Although the embodiment of the present application has been describedabove, a variety of design modifications are possible without departingfrom the gist of the present application.

For example, the material of the electrically insulative sheet 22 is notlimited to PP or PPS as described in the embodiment. It is sufficientthat the electrically insulative sheet 22 be formed of a material havingan electrically insulating property.

The heat transfer sheet 21 may be formed of a porous material into whichwater or the like can easily permeate (for example, foamedpolyurethane). In this case, since the heat transfer sheet 21, which ispositioned on a lower plane of the battery module 13, is formed of aporous material, the water having condensed can be held by the heattransfer sheet 21 and prevented from flowing downward. Thus, occurrenceof the ground fault can be suppressed.

The heat transfer sheet 21 may have grooves on the electricallyinsulative sheet 22 side. In this case, since drains are defined by theelectrically insulative sheet 22 together with the grooves, flows of thewater having condensed and not having been absorbed can be preventedfrom joining one another on the electrically insulative sheet 22.

A battery cooling structure according to an aspect of the embodimentcools a battery module including a plurality of battery cells arrangedside by side and a cooling surface. The battery cooling structureincludes a cooling plate that supports the cooling surface of thebattery module. Heat generated in the battery module is transferred fromthe cooling surface to the cooling plate so as to cool the batterymodule. The battery cooling structure also includes an electricallyinsulative sheet having an electrical non-conductivity and is disposedbetween the cooling surface of the battery module and the cooling plate.

Thus, the battery module of the embodiment can be cooled by transferringthe heat generated in the battery module from the cooling surface to thecooling plate. Also, even when a water drop formed by condensationadheres to the surface of the battery module, the electricallyinsulative sheet prevents the water drop from flowing toward the coolingplate side, and accordingly, a ground fault between the battery moduleand the cooling plate can be prevented from occurring.

The electrically insulative sheet of the embodiment may have a side wallportion, which is formed along sides of the battery module so as toextend upward from an outer periphery of the electrically insulativesheet, so that the electrically insulative sheet has a tray shape.

The electrically insulative sheet of the embodiment holds the water droptherein, thereby preventing the water drop from flowing toward thecooling plate side. Thus, the ground fault can be more reliablyprevented from occurring.

The electrically insulative sheet of the embodiment may be formed of awater repellent material.

Thus, a situation in which the water drop formed by condensation isbrought into contact with the surface of the electrically insulativesheet is unlikely to occur, and accordingly, the ground fault can bemore reliably prevented from occurring.

The battery cooling structure of the embodiment may further includes aheat transfer sheet, which is sandwiched between the cooling surface ofthe battery module and the cooling plate, is deformable by a pressureapplied to the heat transfer sheet, and has a water absorbing property.

Thus, by deformation of the heat transfer sheet, formation of a gapbetween the cooling surface of the battery module and the cooling platecan be prevented. This allows heat generated in the battery module to beefficiently transferred from the cooling surface to the cooling platethrough the heat transfer sheet, and accordingly, an effect by which thebattery module is cooled can be improved. Furthermore, since the heattransfer sheet, which has a water absorbing property, holds therein thewater drop formed by condensation, thereby making it unlikely that thewater drop formed by condensation flows out of the electricallyinsulative sheet. Thus, the ground fault can be more reliably preventedfrom occurring.

The heat transfer sheet of the embodiment may have a groove formedtherein on the electrically insulative sheet side thereof.

Thus, since a drain is defined by the electrically insulative sheettogether with the groove, flows of the water having condensed and nothaving been absorbed are prevented from joining one another on theelectrically insulative sheet.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A battery cooling structure comprising: a coolingplate to support a cooling surface of a battery module to cool thebattery module including a plurality of battery cells arranged side byside; and an electrically insulative sheet having an electricalnon-conductivity and disposed between the cooling surface of the batterymodule and the cooling plate to transfer heat from the cooling surfaceto the cooling plate, wherein the electrically insulative sheet has atray shape and includes a bottom wall portion disposed between thecooling surface of the battery module and the cooling plate, and sidewall portions provided along lateral sides of the battery module toextend upward from an outer periphery of the bottom wall portion, theside wall portions extending continuously about an entirety of the outerperiphery of the bottom wall portion, wherein the tray shape of theelectrically insulative sheet is configured to receive a lower end ofthe battery module such that the side wall portions extend upward alongside walls of the battery module.
 2. The battery cooling structureaccording to claim 1, wherein the electrically insulative sheet is madeof a water repellent material.
 3. The battery cooling structureaccording to claim 1, further comprising: a heat transfer sheet providedbetween the cooling surface of the battery module and the cooling plateand having a water absorbing property, the heat transfer sheet beingdeformable by a pressure applied to the heat transfer sheet.
 4. Thebattery cooling structure according to claim 3, wherein the heattransfer sheet includes a first surface in contact with the coolingsurface of the battery module, a second surface provided opposite to thefirst surface to be in contact with the electrically insulative sheet,and a groove provided on the second surface.
 5. The battery coolingstructure according to claim 1, wherein the side wall portions include afirst side wall portion provided along a first lateral side of thebattery module to extend upward from the outer periphery of the bottomwall portion, and wherein the side wall portions include a second sidewall portion provided along a second lateral side of the battery moduleto extend upward from the outer periphery of the bottom wall portion. 6.The battery cooling structure according to claim 5, wherein the sidewall portions include a third side wall portion provided along a thirdlateral side of the battery module to extend upward from the outerperiphery of the bottom wall portion, the third side wall being oppositeto the first side wall portion with respect to the battery module. 7.The battery cooling structure according to claim 6, wherein the sidewall portions include a fourth side wall portion provided along a fourthlateral side of the battery module to extend upward from the outerperiphery of the bottom wall portion, the fourth side wall portion beingopposite to the second side wall portion with respect to the batterymodule.
 8. A battery cooling structure comprising: a cooling plate tosupport a cooling surface of a battery module to cool the battery moduleincluding a plurality of battery cells arranged side by side; and anelectrically insulative sheet having an electrical non-conductivity anddisposed between the cooling surface of the battery module and thecooling plate to transfer heat from the cooling surface to the coolingplate, wherein the electrically insulative sheet has a tray shape andincludes a bottom wall portion disposed between the cooling surface ofthe battery module and the cooling plate, and side wall portionsprovided along lateral sides of the battery module to extend upward froman outer periphery of the bottom wall portion, wherein the tray shape ofthe electrically insulative sheet is configured to receive a lower endof the battery module such that the side wall portions extend upwardalong side walls of the battery module, and wherein the electricallyinsulative sheet includes a retainer extending upward from one of theside wall portions and having a retainer hole in which a retainingprotrusion of the battery module is provided.
 9. The battery coolingstructure according to claim 1, wherein gaps are provided between theside wall portions and the battery module.
 10. The battery coolingstructure according to claim 1, wherein battery module engages with andretains the electrically insulative sheet such that the electricallyinsulative sheet is detachable and attachable with respect to thebattery module.
 11. The battery cooling structure according to claim 1,wherein the bottom wall portion of electrically insulative sheet extendsparallel to the cooling surface of the cooling plate.
 12. The batterycooling structure according to claim 1, wherein the bottom wall portionof electrically insulative sheet is in direct contact with the coolingsurface of the cooling plate.
 13. The battery cooling structureaccording to claim 1, wherein the electrically insulative sheet issandwiched between the cooling surface of the battery module and thecooling plate.